When electro-excited, an organic electroluminescent device will generate 25% of singlet state and 75% of triplet state. Because of being spin-forbidden, traditional fluorescent material can only utilize 25% of single state excitons, and thus the external quantum efficiency is only limited within 5%. Almost all triplet state excitons may be lost only in the form of heat to enhance the efficiency of organic electroluminescent devices, and the triplet state excitons needs to be fully utilized.
Researchers have put forward many methods for utilizing the triplet state excitons. The most prominent one is the utilization of phosphorescent material. Phosphorescent material, into which heavy atoms are introduced, has a spin-orbit coupling effect. Thus, 75% of triplet state may be fully utilized so that 100% of internal quantum efficiency is achieved. However, rare heavy metals which are expensive are used in the phosphorescent material, which is disadvantageous to the reduction of cost of products. If fluorescent devices can make good use of triplet state excitons, this problem may be dissolved very well. Researchers have proposed the generation of the singlet state by the triplet state annihilation in a fluorescent device to improve the efficiency of the fluorescent device. However, the maximum external quantum efficiency that may be theoretically achieved by this method is only 62.5% which is much lower than that of the phosphorescent material. Thus, it is very necessary to find a new technology to make full use of triplet state energy level of the fluorescent material in order to enhance the light-emitting efficiency.